DOWNING STREET has been forced to defend David Cameron’s decision to involve Scotland Yard in a review of the Madeleine McCann case amid allegations that the Prime Minister’s intervention was a “PR exercise”.

Lord Harris of Haringey, a member of the Metropolitan Police Authority, said the intervention undermined the independence of the force and the investigation would use up valuable resources.

“While no-one doubts the desirability of doing what can sensibly be done to find out what has happened to Madeleine McCann, I can imagine that the senior leadership of the Metropolitan Police are not exactly happy about this,” said the Labour peer.

“It again embroils their officers in a high-profile investigation where the chances of success are unclear, and which will divert limited investigative resources away from other matters.”

He went on: “This is in response to an open letter in The Sun and is entirely predictable in terms of the ‘pulling power’ of News International on Government policy.”

Lord Harris added: “However, his intervention drives a coach and horses through the draft protocol issued by the Home Office designed to preserve the operational independence of the police.”

“What appears on the face of it to be fairly innocuous orders, it’s a fairly short step from there to telling the police they have got to investigate this rather than that.”

The Liberal Democrat peer was among those who this week inflicted a Lords defeat on the UK Government’s plans for directly elected police commissioners in England.

He noted: “This did take place in Portugal where the Met’s writ doesn’t run. I doubt if they have got many Portuguese-speaking officers. I don’t believe that our police can investigate the Portuguese police force.”

As a result, he said: “It becomes a PR exercise.”

Responding to the couple’s plea for help, Mr Cameron had said: “Your ordeal is every parent’s worst nightmare and my heart goes out to you both.”

The Prime Minister’s spokesman said Mr Cameron and Home Secretary Theresa May asked for the review of evidence after the appeal from the McCann family because of the “exceptional” nature of the case.

“There has been a huge amount of public interest in this case since it began, Madeleine McCann has been missing for a long time, there is the international dimension,” he said.

The spokesman also denied Mr Cameron and Mrs May had been directing police on an operational matter, saying: “It was done at the request of the Home Secretary. It was agreed by Sir Paul Stephenson. That is not a direction.”

Last night, a Met spokesman said: “The commissioner was not ordered by the Prime Minister or Home Secretary to provide expertise to the Madeleine McCann case.

“He received a request, which he considered, and took the decision that on balance it was the right thing to do.

“This was subject to funding being made available by the Home Office, as this case is beyond the MPS’s jurisdiction.”

Kate and Gerry McCann described the Met review as “a step in the right direction” and dismissed criticism of it.

Mr McCann, who is originally from Glasgow, said: “I’m sure it will go a long way to [addressing] one of our key disgruntlements, which was that British police had lots and lots of information and it was just sitting there and no-one was looking at it. We are pleased and would like to thank David Cameron for his intervention.”